Emergency department (ED) visits are not distributed equally amongst all patients; approximately 8% of patients are responsible for 28% of all ED visits.2-4 Frequent users of ED services are of significant concern as their healthcare needs are not adequately being met by the standard care system resulting in increased healthcare costs and the potential to impact the quality of care provided to all ED patients.1 While frequent ED users are a heterogeneous population, little is known about ways to classify frequent ED users along resource use into specific groups amenable to goal-directed interventions. Understanding frequent ED user groups will guide the development of targeted interventions to effectively assist these complex patients, improve the quality of patient care, and lower healthcare resource use. The Denver Health Medical Center, a model public, academic healthcare system, 40 recently created an ambulatory intensive caring unit, the DHMC Intensive Outpatient Clinic (IOC), in which high-utilizing patients receive all of their outpatient care in the IOC. The goal o the clinic is to maintain a high quality of care and decrease hospitalizations. We believe that the IOC is a prime target for evaluation as a natural experiment to assess whether components of the IOC are effective at reducing recurrent ED visits and avoiding overutilization of healthcare resources. The first hypothesis is that distinct categories of frequent ED users with differing characteristics and clusters of ED resource use exist that will be amenable to tailored, targeted interventions to reduce healthcare resource use and improve the quality of patient care. The second hypothesis are that specific IOC services provided to frequent ED users do result in fewer ED visits and that the IOC will be demonstrated to have reach, efficacy, adoption, implementation, and maintenance for frequent ED users. The third hypotheses are that a pilot intervention for frequent ED users will be feasible in the Denver Health ED; the intervention will be adopted and achievable in the ED while being useful and timely for providers and participants. The Specific Aims therefore include: (1) to create a taxonomy of frequent ED users and the services they utilize; (2) refined by the taxonomy identified in Aim 1, to evaluate the impact of the DHMC IOC on frequent ED visits; and (3) to design and implement a pilot intervention in the Denver Health ED targeted specifically at decreasing ED visits and avoiding overutilization based upon lessons learned from the IOC.